Kept rolling off the regular mummy XTherm NXT, which is under 50 cm wide around the hips, and switched to the wide version; blames the vertical air channels when a side sleeper's hip goes past the edge. Has no such problem on a similarly sized NEMO Tensor Elite.
“The regular mummy shaped one Xtherm NXT is less than 50 cm around the area where you hip typically will be. I was rolling off the side of mine.”